Auto merge of #110319 - ferrocene:pa-more-ignore-reasons, r=ehuss

[compiletest] Add more test ignore reasons, `needs-` validation, and improved error messages

This PR makes more improvements to the way compiletest ignoring headers are handled, following up on #108905:

* Human-readable ignore reasons have been added for the remaining ignore causes (`needs-*` directives, `*llvm*` directives, and debugger version directives). All ignored tests should now have a human-readable reason.
* The code handling `needs-*` directives has been refactored, and now invalid `needs-*` directive emit errors like `ignore-*` and `only-*`.
* All errors are now displayed at startup (with line numbers) rather than just the first error of the first file.

This PR is best reviewed commit-by-commit.

r? `@ehuss`

Author: bors